1. Field of the Invention
The present invention relates to an image forming apparatus using elecrophograpic process such as a copying machine, printer, facsimile, specifically to an image forming apparatus in which the amount of developer of each color can be detected by a single detecting sensor when forming color images.
2. Description of the Related Art
Generally, in image forming apparatuses such as copying machines, printers, or facsimiles, an image retaining member such a photoreceptor drum is uniformly exposed, then an electrostatic latent image is formed on the photoreceptor drum by exposing it corresponding to image data, and the electrostatic latent image is developed by a development apparatus to form a toner image on the photoreceptor drum. Then the toner image is transferred onto a recording sheet of paper and fused by a fusing device and the sheet of paper is discharged to a catch tray.
In these image forming apparatuses, toner is supplied to the development apparatus from a toner tank provided separate from the development apparatuses or development cartridges, and toner supply is controlled by detecting the amount of toner in the development apparatus or development cartridge when supplying toner thereto from the toner tank.
Optical sensors are used to detect the amount of toner in a development apparatus, for example. In order to detect accurately the amount of toner remaining in three hoppers provided in a development cartridge, a mirror, half mirrors, and windows are provided to the partition walls of the hoppers the light emitted from a light emitting means located outside the development cartridge is reflected from the mirror and half mirrors and received by three light receiving means located outside the development cartridge, and the amount of toner in each of the hopper is evaluated based on the time the reflected light is detected per unit time by each of the light receiving devices, thus the amount of toner in a cartridge is detected multiple-step wise and accordingly accurately (see JP2001-215784 A (patent literature 1)).
In this apparatus when applied to a color image forming apparatus, there are provided a plurality of development cartridges, each of the development cartridges being provided with a plurality of agitation members for stirring the toner in three hoppers in the cartridge, a cleaning means being provided at the end of each agitation member; and at least one light emitting means and at least one light receiving means that are located so that the light emitted from the light emitting means passes through at least one hopper and the light reflected from the mirror or half mirrors is received by the light receiving means, thereby the amount of toner remaining in the cartridge being detected. Further, a light reflecting means is provided in the development cartridge accommodating section to enable detection of the presence or absence of the cartridge in addition to detection of the amount of toner remaining in the cartridge.
However, in the image forming apparatus disclosed in patent literature 1, although the amount of toner remaining in the development cartridge of each color can be determined multiple-step wise and also the presence or absence of cartridge can be discerned, it is necessary to provide a set of remaining toner amount detection sensor including a light emitting means and a plurality of light receiving means for each of the development cartridges, which causes increase in cost.
Further, in the image forming apparatus of patent literature 1, a light reflecting means is needed to provide in the development cartridge accommodating section, which also causes increase in cost of the apparatus. Furthermore, as a plurality of mirrors and half mirrors are used in this apparatus, optical paths are complicated, and when malfunction occurs to any one of them, detection of the amount of toner remaining in the cartridge will fail.
As mentioned above, there is a disadvantage in the image forming apparatus of patent literature 1 that the amount of toner in the development cartridges and whether the cartridge is attached to or detached from the development apparatus can not be detected by a single remaining toner amount detection sensor device.